Cabin Noise Research Articles

Broadband Active Noise Control Design through Nonsmooth H∞ Synthesis

This paper deals with active control of a broadband noise in a car cabin. It aims to study the achievable performance of such control in the SISO feedback case. The main limitations involved, known as waterbed effect, are critical for such problem due to the presence of non-minimum phase zeros. To evaluate the intrinsic limitations due to these non-minimum phase zeros, a multi-objective control synthesis is proposed, allowing to cope with classical speciffications (performance and robustness), without pessimism. The control synthesis is based on a H∞ criterion to be minimized under some decoupled constraints. It consists in a non-convex and non-smooth optimization problem, for which a local optimum may be efficiently obtained. A particular control structure is considered in order to reduce the number of decision variables, to set relevant bounds on these parameters and to choose appropriate initial conditions. Then the optimization problem is solved using recent results on non-smooth optimization. The whole design process is detailed, including the identiffication of the synthesis model. The control strategy is then applied to an instrumented cavity, which shares most of the acoustic characteristics of a car cabin. Finally, the analysis of the results gives clear conclusions on SISO feedback possibilities, and paves the way for an efficient multivariable design case.

機関防振装置と電気推進船への適用事例紹介

Recently, the demand for a low noise environment in vessels has increased. Cabin noise consists of several noise sources. In most cases, the primary source of noise is the engine. Generally, the vibration isolator is effective in reducing structure-borne noise. This paper presents three types of vibration isolators for reciprocating engines and application examples for electric propulsion systems.

A crossmodal role for audition in taste perception.

Our sense of taste can be influenced by our other senses, with several groups having explored the effects of olfactory, visual, or tactile stimulation on what we perceive as taste. Research into multisensory, or crossmodal perception has rarely linked our sense of taste with that of audition. In our study, 48 participants in a crossover experiment sampled multiple concentrations of solutions of 5 prototypic tastants, during conditions with or without broad spectrum auditory stimulation, simulating that of airline cabin noise. Airline cabins are an unusual environment, in which food is consumed routinely under extreme noise conditions, often over 85 dB, and in which the perceived quality of food is often criticized. Participants rated the intensity of solutions representing varying concentrations of the 5 basic tastes on the general Labeled Magnitude Scale. No difference in intensity ratings was evident between the control and sound condition for salty, sour, or bitter tastes. Likewise, panelists did not perform differently during sound conditions when rating tactile, visual, or auditory stimulation, or in reaction time tests. Interestingly, sweet taste intensity was rated progressively lower, whereas the perception of umami taste was augmented during the experimental sound condition, to a progressively greater degree with increasing concentration. We postulate that this effect arises from mechanostimulation of the chorda tympani nerve, which transits directly across the tympanic membrane of the middle ear.

트랙터 운전실의 소음 저감에 관한 연구

This study focused on identifying the major noise source in a tractor cabin using experimental methods. The noise levels in a tractor cabin for different engine revolution speeds were analyzed to identify the noise source. The results showed that the power steering unit (PSU) was the major noise source in a tractor cabin. The PSU was moved to the outside from the inside of the cabin in order to reduce the noise in the tractor cabin. As a result, the noise levels on the left and right sides of the operator in the tractor cabin were reduced by 6.8 and 3.9 dB, respectively. Finally, the window method was introduced to evaluate the contribution of the transmission noise. The orders of significance in the tractor noise were the front, bottom, and left area, successively.

Structural-acoustic coupling study of tyre-cavity resonance

The tyre cavity resonance induced cabin noise has been a major unsolved customer complaint issue for a long time. A study of coupled tyre-cavity structural-acoustic system using impedance compact mobility matrix is presented in this paper. This method offers a better physical interpretation and numerical prediction about a coupled tyre-cavity system than previous models. It can calculate the sound pressure inside the tyre cavity as well as the tread wall vibration velocity at the same time. The analytical results have been verified by the results of the VAOne vibro-acoustic model. The VAOne software was also validated by the results from a case study of a rectangular box-cavity system in previous literature. From the analytical calculation, the tyre cavity coupling modal frequency is found to be split into two close resonance frequencies if the tyre structural natural frequency is close to the fluid cavity resonance frequency. The geometric coupling coefficient has been calculated using Matlab code. This study provides a better insight into the resonance coupling phenomenon of the tyre cavity to the tyre structure and its root causes. It demonstrates more clear physical meaning of the tyre cavity coupling model and its inherent characteristics than that from ‘black box’ finite element software. This develops a better understanding of the problem and its root causes facilitates effective solutions for the problem. Even though the study was conducted in a tyre-cavity system, the solution and methodology are applicable to other toroidal shape structural-acoustic systems.

Amar Gopal Bose

Amar Gopal Bose

Altitude and airspeed effects on the optimum synchrophase angles for a four-engine propeller aircraft

Abstract Noise and vibration is a serious problem in all types of aircraft. Any techniques that lower cabin noise and vibration levels by even a few decibels with little or no weight or performance penalties are worth pursuing. Propeller synchrophasing is one such technique that has shown potential in aircraft with two or more propellers; however this technique is not being used to its full potential because the synchrophase angles are typically fixed. This paper provides a detailed examination of how the optimum synchrophase angles in a typical four-engine propeller aircraft vary with different altitudes and airspeeds, and how this information could lead to the design of new adaptive propeller synchrophasing systems and potentially yield improvements to other active noise control measures in propeller aircraft.

Assessing the Aeroacoustic Response of a Vehicle to Transient Flow Conditions from the Perspective of a Vehicle Occupant

On-road, a vehicle experiences unsteady flow conditions due to turbulence in the natural wind, moving through the unsteady wakes of other road vehicles and travelling through the stationary wakes generated by roadside obstacles. Separated flow structures in the sideglass region of a vehicle are particularly sensitive to unsteadiness in the onset flow. These regions are also areas where strong aeroacoustic effects can exist, in a region close to the passengers of a vehicle. The resulting aeroacoustic response to unsteadiness can lead to fluctuations and modulation at frequencies that a passenger is particularly sensitive towards. Results presented by this paper combine on-road measurement campaigns using instrumented vehicles in a range of different wind environments and aeroacoustic wind tunnel tests. A new cabin noise simulation technique was developed to predict the time-varying wind noise in a vehicle using the cabin noise measured in the steady environment of the wind tunnel, and a record of the unsteady onset conditions on the road, considering each third-octave band individually. The simulated cabin noise predicted using this quasi-steady technique was compared against direct on-road cabin noise measurements recorded under the same flow conditions to assess the response of the vehicle to oncoming flow unsteadiness. The technique predicted the modulation of the wind noise under unsteady on-road conditions with good fidelity. This is because the cabin noise response to oncoming flow unsteadiness remained generally quasi-steady up to fluctuation frequencies of approximately 2 to 5 Hz, with fluctuations at higher scales having a progressively smaller impact, and because most of the onset flow fluctuation energy on the road occurs at frequencies below this threshold. The relative impact of the baseline level of cabin noise and the sensitivity of the cabin noise to changes in yaw angle were assessed in terms of occupant perception and this highlighted the importance of modulation. This can provide guidance when assessing the on-road wind noise performance of vehicle geometry modifications and of different vehicles.

Improved sound transmission loss in an automotive component using piezoceramic patches and dissipative shunt circuits

Noise in a vehicle is generally caused by the vibration of various automotive components, such as the dashboard, door panels, and roof. For example, vibrations caused by the engine may cause a dash panel to vibrate leading to noise in the vehicle cabin. The control of such noise and vibration may be achieved by placing a viscoelastic or other suitable damping material on the automotive component; however, conventional damping materials usually have a high density, which can lead to significant increases in the overall mass of the sound insulation system. A lightweight alternative employs piezoceramic patches connected to a resistor–inductor circuit, where the mechanical vibration, converted into electrical energy by the piezoceramic, is dissipated in the form of thermal heat through the resistor. The presence of an inductive element allows the system to perform in the vicinity of a mode of the vibrating structure, in an effect similar to a resonant vibration absorber. In this work, the damping capacity of this resonant electrical circuit is demonstrated in a dash panel installed between coupled reverberant and anechoic rooms for assessments of sound transmission loss. Finite element simulation and theoretical analysis are used to support the choice of the electrical component values and the correct placement for piezoelectric patches. The resulting sound transmission control is compared to baseline measurements with conventional viscoelastic material thermally bonded to the panel surface. The work is concluded with a discussion on the achieved results and mass saving benefits of the proposed damping technique.

A fully coupled finite element-boundary element vibro-acoustic analysis for laminated composite structures with enclosed acoustic cavities

A major contribution of aircraft cabin noise is due to the vibrating airframe structure in which the use of lightweight composite materials is quite common. Due to the strong influence of such vibrating structures on the enclosing fluid, such as air, and vice-versa, a fully coupled analysis involving both the systems is necessary in many cases. Hence the present work details a fully coupled vibro-acoustic analysis of such type of flexible cavity subjected to the external mechanical excitation based on a coupled finite element (FE) and boundary element (BE) approach. The structural mode shapes and eigen frequencies are computed using the FE free vibration analysis of in-vacuo structures, which are subsequently coupled through the mobility equation with the acoustic part modeled with the BE method. The developed approach is also well compared with the fully coupled FE approach but the advantage derived here is that it is sufficient to model each domain independently thus reducing the problem dimension. The discussed method ensures full coupling between the two systems considering the cavity acoustic back pressure and also enables a fully coupled analysis of a double-walled structure attached to an acoustic cavity which resembles a true aircraft cabin.

Tiltrotor cabin noise control through smart actuators

This paper deals with the abatement of the tonal noise inside the fuselage of a mid-range tiltrotor aircraft, as generated by the propulsive system. The problem is basically multidisciplinary, involving interactions among the exterior noise field, elastic fuselage dynamics, interior acoustics and control system. A stiffened fuselage, with piezoelectric patches embedded into the structure, is supposed to be impinged on by the aeroacoustic field generated by propellers and excited by the wing/pylon/proprotor vibratory loads at the wing–fuselage attachment. An optimal linear quadratic regulator cyclic control formulation, coupled with a genetic optimization algorithm, is applied to synthesize the control law driving the smart actuators so as to alleviate cabin noise. The aeroacoustoelastic model considered in the control problem is obtained by combining cabin interior acoustics, fuselage smart shell dynamics and wing/pylon/proprotor aeroelasticity described through modal approaches with the exterior pressure field provided by boundary element method solvers. Numerical results examine the effectiveness and robustness of the proposed active control strategy.

Improvement of noise reduction performance for a high-speed elevator using modified active noise control

A high rise building demands a high-speed elevator. Since a high-speed elevator has various transfer paths of noise transmitted from motor and rope to cabin interior, it is very difficult to solve the noise problem. Most research for noise reduction has been performed regarding passive noise control by using mainly absorption material and insulation material. In this study, while it is modeling as multiple-input and single-output with respect to transfer paths of high-speed elevator on conditions of stationary and driving states, the characterized frequency in the cabin is discovered through a contribution technique. It is able to replace by 1-dimensional model to control noise at a major contributed frequency. Also, a new active noise control technique has been proposed to control the cabin noise effectively at unpleasant area that is required to make quite zone for passenger. The Correlation Filtered X-LMS (Co-FXLMS) algorithm has been applied to control the dominant frequency noise that it has a high contribution. Simultaneously, this study has a proposed Moving Band Pass Filter (MBPF) to improve the performance of active noise control in the cabin which is able to apply a dynamic system with time variant states. Finally, we obtained the 8dB noise reduction in the cabin at ear level and it has been proved that the modified active noise control using Co-FXLMS algorithm and MBPF is available to improve the performance of noise reduction.

中高速機関の騒音対策

Recently, the demand for a low noise environment in vessels has increased. Cabin noise consists of several noise sources. In most cases, the primary source of noise is the engine. Generally, the resilient mount system is effective in reducing Structure-borne Noise, especially in middle and high speed engines. This paper presents collaborative strategies by a ship builder and an engine maker to reduce Cabin noise in a tourist ship with some applications.

Study on the Vehicle Cabin Noise Employing the Interfacial Friction in Double Layered Frames Used in Electric Vehicle Traction Motors

Study on the Vehicle Cabin Noise Employing the Interfacial Friction in Double Layered Frames Used in Electric Vehicle Traction Motors

Prediction and Control of 32m Z-Propeller Tug Cabins Vibration and Noise

Based on statistical energy analysis method, the 32m z-propeller tug model was built by VA One software. The numerical simulation research of vibration and noise of 32m z-propeller tug cabin was carried out by VA One. In order to prove the numerical simulation validity, the simulation data was compared with that of the experiments, which shows that the vibration prediction error is lower than 15% and the noise prediction error is about 5 dB(A). Whats more, schemes of cabin noise reduction and the power plant vibration isolation were designed to make the vibration and noise levels meet the IMO and GB5980-2000 standards requirements. The sound absorption material was pasted on the bulkhead of cabins, and the average noise reduction level achieved to 7 dB(A). Then, the single-layer vibration isolation system was designed for the diesel engines, the average noise reduction level achieved to 5 dB(A). The simulations have some guiding values on the control of tug cabins vibration and noise.

Evaluation of the Aerodynamic and Aeroacoustic Response of a Vehicle to Transient Flow Conditions

A vehicle on the road encounters an unsteady flow due to turbulence in the natural wind, unsteady wakes of other vehicles and as a result of traversing through the stationary wakes of roadside obstacles. Unsteady effects occurring in the sideglass region of a vehicle are particularly relevant to wind noise. This is a region close to the driver and dominated by separated flow structures from the A-pillar and door mirrors, which are sensitive to unsteadiness in the onset flow. Since the sideglass region is of particular aeroacoustic importance, the paper seeks to determine what impact these unsteady effects have on the sources of aeroacoustic noise as measured inside the passenger compartment, in addition to the flow structures in this region. Data presented were obtained during on-road measurement campaigns using two instrumented vehicles, as well as from aeroacoustic wind tunnel tests. Conventional admittance functions relating oncoming flow yaw angle to cabin noise response are generally not suitable due to the non-linear steady state characteristics obtained in the wind tunnel, i.e. the cabin noise does not vary with yaw angle in a linear fashion under steady-state conditions. Therefore two alternative approaches were used based on instantaneous conditions to determine a quasi-steady predicted cabin noise time-history. These techniques demonstrated that the cabin noise response to oncoming flow unsteadiness remained generally quasi-steady up to fluctuation frequencies of approximately 2 to 5 Hz, where above this smaller flow scales have a progressively smaller impact on cabin noise fluctuations. Therefore, with a measurement of both the cabin noise in the steady environment of the wind tunnel and the unsteady onset flow conditions, the fluctuations (and thus the modulation) of the wind noise under these unsteady conditions is able to be predicted.

Using the effect of alcohol as a comparison to illustrate the detrimental effects of noise on performance

The aim of the present research is to provide a user-friendly index of the relative impairment associated with noise in the aircraft cabin. As such, the relative effect of noise, at a level typical of an aircraft cabin was compared with varying levels of alcohol intoxication in the same subjects. Since the detrimental effect of noise is more pronounced on non-native speakers, both native English and non-native English speakers featured in the study. Noise cancelling headphones were also tested as a simple countermeasure to mitigate the effect of noise on performance. A total of 32 participants, half of which were non-native English speakers, completed a cued recall task in two alcohol conditions (blood alcohol concentration 0.05 and 0.10) and two audio conditions (audio played through the speaker and noise cancelling headphones). The results revealed that aircraft noise at 65 dB (A) negatively affected performance to a level comparable to alcohol intoxication of 0.10. The results also supported previous research that reflects positively on the benefits of noise cancelling headphones in reducing the effects of noise on performance especially for non-native English speakers. These findings provide for personnel involved in the aviation industry, a user-friendly index of the relative impairment associated with noise in the aircraft cabin as compared with the effects of alcohol. They also highlight the benefits of a simple countermeasure such as noise cancelling headphones in mitigating some of the detrimental effects of noise on performance.

Optimisation of acoustical comfort in vehicle cabin using the goal programming

Car cabin acoustical comfort is one of the main features that may attract customers to purchase a new vehicle. The noise in a passenger car cabin is closely related to the vibration generated in the vehicle system. In this study, the effects of vibration on noise in the passenger car cabin have been studied. The vehicle acoustical comfort index (VACI) was used to evaluate the noise annoyance level and the vibration dose value (VDV) was used to evaluate the vibration level. Because engine noise is one of the dominant sources of interior noise, an approach has been used to study the correlation between engine speed and the level of generated vibration. According to the changes in the noise and the vibration level as a function of engine speed, a goal programming model was used to optimise the noise annoyance level in the passenger car cabin. At the end of the study, a multi-objective model was successfully built to optimise the noise annoyance levels by looking at the required vibration dose value at certain engine speeds.

Development of Compact Size Onboard Device for Condition Monitoring of Railway Tracks

This paper summarizes a new development of a compact size onboard device for condition monitoring of railway tracks followed by a former development of a portable onboard device. Track irregularities are estimated from a vertical and lateral acceleration and roll rate of a car body. Rail corrugation is detected from cabin noise with spectral peak calculation. A GPS system and a map-matching algorithm are used to pinpoint the location of faults on tracks. The device is driven by Li-ion battery for 6 hours or outside power source. Accelerometers, rate gyroscope and GPS were redesigned to give higher performance. One can add a microphone outside if a condition monitoring of rail corrugation is necessary. Collected data are usually kept in an inside un-volatility memory (SSD) or a SD card. Communication unit transfers the collected data to a data server via cellular phone. The compact size onboard devices provide regular monitoring of tracks for sustaining railway system with securing safety.

Noise annoyance fuzzy index in passenger car cabin

Vehicle acoustical comfort and vibration in passenger car cabin are the factors which attract buyers to a vehicle, in order to have a comfortable driving environment. The comfort of the driving will affect the driver by influencing their driving performance. Vehicle acoustical comfort index (VACI) has been introduced to represent the level of annoyance in passenger car cabin. This index has been used in the computation related to the acoustics aspect in the car cabin. Noise annoyance is categorised into five states: most annoying, medium annoying, marginal, medium pleasant and most pleasant. In order to improve the VACI index, this study carries out an approach to classify and categorise the aforementioned five states using the fuzzy set theory approach. At the end of several studies, the noise annoyance fuzzy index (NAFI) has been introduced. By using NAFI, automotive researchers will be able to classify and make judgement about the state of annoyance from the exposed noise in the car cabin numerically, where the use of this index is regarded to be more precise and has practically been used in engineering fields especially where the fuzzy logic system is concerned.